Stereotype mat



United States Patent STEREOTYPE MAT Russell 'R. Eichmeier, Freeport,111., assignor to B urgess Cellulose Company, Freeport, Ill.,1acorporation of Delaware No Drawing. Continuation .of application SerialNo. 170,030, June 23,1950. This application January 10, 1955, Serial No.481,009

8 Claims. (Cl. 106-385) This invention relates to improvements instereotype mats and particularly to an improvement in the composition ofstereotype mats wherebythe molding and casting properties thereof areimproved.

The stereotype mat of the type which is in common use and to which thepresent invention relates consists of a relatively thick sheet of feltedcellulose fibers, such as rag stock, cotton linters, chemical wood pulp,such as alpha, sulphite or soda pulp, or the like. The stereotype matusually contains a filler, such as powdered clay, talc, etc. mixed withthe fibers in the body of the mat. A stereotype mat of this generalcharacter is described in ice type mat is composed of felted cellulosefibers. Cellulose v fibers, in themselves, possess only a limited amountof plasticity, the impression being accomplished by reason of thecompression and stretch undergone by the felted mass of ,the'fibers. Asheet of felted cellulose fibers normally exhibits characteristiclimitations with respect to such compression and stretch, and thepresent invention has for its principal purpose the modification of themat whereby its plasticity when moist is substantiallyimproved. .Theresult is that during manufacture the surface of the mat is readily madesmooth and free of projecting fibers and United States Patent 1,524,155.The surface ofvthe mat which is'to receive the impression of the formmay have a coating applied to it to enhance its smoothness anduniformity. The coating composition may consist of an aqueous suspensionof starch, dextrin, clay or the like, a suitable composition for thispurpose being described in United States Patent 1,863,731.

An essential property of a stereotype mat is that it readily absorbswater, and it is usually stored shipped .in humidified condition with awater content of about 10% to 50%, based on the total weight of the mat.In this moistened condition it is ready for use and the form or patterncontaining the type, cuts, etc., is impressed upon it. Itsmoist-plasticity enables it to take a well-defined impression of theform, including the details thereof.

After the impression has .been taken, the mat .is dried by subjecting itto heat in what is called a scorcher. In this operation all of themoisture is rapidly driven out of the mat. An important property of themat is that it permits the moisture to escape readily during this dryingoperation. After it is dry, the surface carrying the impression is hardand very smooth for the reception of the molten type metal.Reproductions of the original form are then made by casting molten typemetal against such surface and allowing the metal-to solidify in thatposition. Since most printing work is done on cylindrical presses, thedried mat is placed in a curved casting box and is bent or curved toconform to the shape of the box. It is highly desirable to make as manyreproductions as possible from the same stereotype mat and this is thereason why the surface should be hard and smooth. If there is anyroughness or fractures, the fibers of the mat project from the surfaceand become embedded in the cast molten metal. After the castingoperation the solidified metal and the mat are separated and if fibersor any portion of the mat surface adheres to the metal the surface istorn andithe useful life of the mat is at an end.

It is the principal object of the present invention to provide astereotype mat of' increased plasticity when moist so as to receive witha minimum of pressure and without fracture a full, exact and faithfulimpression of the type, half-tones, illustrations etc. from the metalform, and to retain this impression without change during the castingoperation whereby a stereotype printing plate is formed which .is anexact and faithful duplicate of the original form. As has been statedheretofore, the stereoduring use it takes a full and exact impressionfrom the form without fracture, whereby a minimum of wear or damage iscaused by casting molten metal against the mat and'the latter has theability to take a large number of casts of superior quality. This is ofespecial importance in newspaper work where a large number of stereotypeplate reproductions are required from each original form.

"It is a further object of the invention to provide a stereotype mathaving the above improved properties and which possesses the full amountof strength for mats of this general character and undergoes the normalamount of shrinkage while being dried.

It is a further object of the invention to provide a mat having theimproved properties described above in which the'moisture is morereadily released during drying of the molded mat, whereby'the latter ismore quickly and easily rendered completely dry and capable of forming aperfect stereotype platereproduction.

It is a furtherobject of theinvention to provide a stereotype mat of thecharacter described which, after it has been molded and dried, possessesincreased flexibility,

without sacrifice of strength or toughness, whereby it more readilyconforms to the curvature of the casting box. 7

Other objects and advantages will become apparent as the followingdescription progresses.

The objects are obtained by incorporating in the body of the stereotypemat a finely divided precipitated alkaline earth metal silicate, thatis, a chemically precipitated silicate of barium, calcium, magnesium, orstrontium. The silicate may be used in place of the filler normally usedin a stereotype mat. It is permissible to use a small amount of normalfiller, but this is not necessary when the alkaline earth metal silicateis incorporated in accordance with the present invention.

There are a number of natural silicates of the alkaline earth metalswhich have been formed by fusion and other natural processes, and thesesilicates are not suitable for the present invention. The precipitatedsilicates are formed by preparing an aqueous solution of a water solublealkaline earth metal compound, and treating the solution with a watersoluble alkali metal silicate. The soluble alkaline earth metal compoundmay be an alkaline earth metal salt or hydroxide, an example of a saltbeing an alkaline earth metal chloride. Examples of suitable watersoluble alkali metal silicates are sodium silicate and potassiumsilicate. A precipitate of the alkaline earth metal silicate is therebyformed, which is separated from the solution, washed with water, driedand ground to a finely divided condition. Finely divided precipitatedalkaline earth metal silicates which are suitable for use are alsoavailable upon the market.

In accordance with the present invention, it has been discovered thatwhen a substantial amount of an alkaline earth metal silicate of thecharacter described is incorporated in a' stereotype mat of feltedcellulose fibers a pronounced increase in the moist-plasticity of themat is obtained, together with the other benefits of improved smoothnessof surface, release of moisture during drying, flexibility when dry,etc., Without any sacrifice in other desirable properties such asstrength, toughness, hardness of surface when dry, normal shrinkage,etc.

The proportion of alkaline earth metal silicate may vary withinrelatively wide limits. Amounts from about to about based on the dryweight of the stereotype mat, have been used with satisfactory results.

The following are several examples of the preparation of a stereotypemat in accordance with the present invention. It is to be understoodthat these specific examples are illustrative only and that theinvention is not limited thereto but changes and modifications may bemade as will occur to those skilled in the art.

Example 1 Calcium silicate is prepared by dissolving 8 parts by weightof calcium chloride, CaClz, in 235 parts of water and slowly adding tothis 83 parts of a water solution of sodium silicate containing 7.3parts of the sodium silicate having the oxides present in the ratio 1NazO, 3.3 SiOz. The reaction solution is heated to boiling. Aprecipitate of calcium silicate is formed having substantially the ratio1 CaO, 3.3 SiOz. After' the reaction is complete, the precipitate isseparated from the solution by filtering and is washed and dried. It isthen reduced by grinding to finely divided particles, a suitableapparatus for this purpose being a ball mill. While the particle size isnot critical, a fineness of the order of that of paper-makers clay ispreferred.

Certain characteristics are given herein for the calcium silicate soformed and for other alkaline earth metal silicates disclosed herein,said characteristics being specific surface area and the presence of asubstantial amount of the silicate in the amorphous state. The specificsurface area is given in terms of square meters per gram and isdetermined by the low temperature nitrogen adsorption method which isdescribed in the article by S. Brunauer, P. H. Emmett and E. Teller atpages 309 to 319 of vol. 60 of the Journal of the American ChemicalSociety. The fact that a substantial amount of the silicate is in theamorphous state is determined by obtaining an X-ray ditfraction patternof the material by the Hull-Debye-Scherrer method described at pages 391to 419 of X-rays in Practice by Wayne T. Sproull. published in 1946 byMcGraw-Hill Book Company, Inc. In such a pattern the presence of aso-called amorphous ring shows that a substantial amount of the silicateis in the amorphous state.

The calcium silicate formed by the method described has a specificsurface area of 45.4 square meters per gram, and a substantial amount ofsaid silicate is in the amorphous state.

The stereotype mat is then formed by a procedure the manipulative stepsof which, except for the inclusion of the alkaline earth metal silicate,follow well known procedure for making stereotype mats. A quantity of anaqueous slurry of coniferous alpha pulp is placed in a beater and beatenuntil the fibers are well separated and there is a suitable hydrationthereof. Calcium silicate such as has been described heretofore is mixedwith the beaten fibers in the water suspension, the proportions, on adry weight basis, being 100 parts of fibers and 23 parts of calciumsilicate. The mass is agitated to form a thorough, intimate mixture ofthe fibers and calcium silicate, and it is then transferred to apaper-making wet machine where it is placed in the usual form of aliquid suspension in water. The mixture of fibers and calcium silicateis felted out in the form of a web upon the screen of the wet machineand the web is transferred to a roll upon which it is wound until asufiicient number of layers have been built up to form a sheet of thedesired thickness. The sheet is then removed from the roll and dried andcompressed to the desired thickness for the stereotype mat. In usualpractice, the thickness of a stereotype mat is about .015 inch to .040inch. The dry stereotype mat may have a coating such as has beendescribed heretofore applied to the surface thereof which is to take theimpression from the form.

For use, the resulting stereotype mat is moistened, so as to containabout 10% to of water, based on the total weight of the mat, whereby itis rendered plastic. A moisture content of about 20% is usuallysatisfactory for this purpose. The stereotype mat containing the calciumsilicate is highly plastic and is of uniform texture and has a verysmooth surface, whereby it takes a deep and exact impression of theprinting form with a moderate amount of pressure. In addition, itreadily releases the moisture upon drying following the taking of theimpression, and has a smooth, hard surface to receive the cast moltenmetal, which surface is free from roughness,

fractures and projecting fibers, whereby a large number of faithful andexact stereotype reproductions may be made from a single stereotype mat,which reproductions carry in sharp definition the details of theoriginal form. in all of these respects, the stereotype mat of thepresent invention is superior to one which does not contain the calciumsilicate but rather contains an ordinary filler.

Example 2 A stereotype mat was made by a procedure similar to that ofExample 1 except that calcium hydroxide, Ca(OH)z, was used in place ofcalcium chloride, CaClz, in the preparation of the calcium silicate. Theproduct so formed has a specific surface area of 10.7 square meters pergram, and a substantial amount of the silicate is in the amorphousstate.

Example 3 A stereotype mat was made by a procedure similar to that ofExample 1 with the exception that sodium metasilicate, having the ratio1 NazO, l SiOz was used in place of the sodium silicate having the ratio1 NazO, 3.3 SiOz.

The calcium silicate formed by this method has a specific surface areaof 105 square meters per gram, and a substantial amount of the silicateis in the amorphous state.

In the some way, stereotype mats were made by the procedures of Examples1 and 2 in which the NazO to SiOz ratio of the sodium silicate wasvaried from 1 NazO, 1 SiOz to 1 NazO, 3.75 SiOz. The CaO to SiOz ratioin the resulting calcium silicate corresponded substantially to the N820to SiOz ratio in the sodium silicate. In every case a satisfactory,improved stereotype mat was obtained. The calcium silicate formed byusing the 1' NazO, 3.75 SiOz ratio has a specific surface area of 54.3square meters per gram, and a substantial amount of said silicate is inthe amorphous state.

In the same way, stereotype mats were made by the procedures describedheretofore employing barium silicate, magnesium silicate, and strontiumsilicate in place of calcium silicate, said silicates being made bysubstituting the corresponding water soluble barium, magnesium orstrontium compound for the water soluble calcium compound used in thedescribed procedures. The barium silicate formed by using bariumchloride and sodium silicate having the ratio of 1 NazO, 3.3 SiOz has aspecific surface area of 25.9 square meters per gram, and asubstantial'amount of said barium silicate is in the amorphous state.The magnesium silicate formed by using magnesium chloride and sodiumsilicate having the ratio 1 NazO, 3.3 SiOz has a specific surface areaof 525 square meters per gram, and a substantial amount of saidmagnesium silicate is in the amorphous state. The strontium silicateformed by using strontium chloride and sodium silicate having the ratio1 NazO, 3.3 SiOz has a specific surface area of 28.2 square meters pergram, and a substantial amount of said strontium silicate is in theamorphous state. Also, stereotype mats were made by the proceduredescribed in Example 1 in which calcium and magnesium silicates obtainedcommercially upon the market were used in place of the calcium silicateprepared by the precipitation step as described in connection withExample 1. Such commercially available silicates are prepared byprecipitation out of an aqueous solution of a calcium or magnesiumcompound, as the case may be. In all cases the stereotype mat had thesuperior properties which have been described heretofore.

One such commercially available calcium silicate which has been used isthat sold under the trademark Silene EF, which has a specific surfacearea of 68.5 square meters per gram, and a substatnial amount of whichis in,

meters per gram, and a substantial amount of which is in the amorphousstate. As stated heretofore, theproportions of the alkaline earth metalsilicate may vary over a considerable range,

and about to 25%, based on the dry weight of the stereotype mat, hasbeen found to be suitable. With respect to the silicates, the ratio ofalkaline earth metal oxide to SiOr; may vary in the same manner asexplained heretofore in connection with calcium silicate. Also, insteadof a single alkaline earth metal silicate, a mixture of several suchsilicates may be used in the stereotype mat. Also, the stereotype matmay be composed'of cellulose fibers different from the coniferous alphafibers used in Example 1, as is explained in the early part of thisspecification.

This application is a continuation of my copending application SerialNo. 170,030, filed June 23, 1950, now abandoned.

What is claimed is:

l. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler, said filler containing as an essentialconstituent, a synthetic precipitated alkaline earth metal silicate,said stereotype mat being characterized by high plasticity when moist.

2. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler, said filler containing, as an essentialconstituent, a synthetic precipitated silicate of a metal from the groupconsisting of barium, calcium, magnesium and strontium, said stereotypemat being characterized by high plasticity when moist.

3. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler, said filler containing as an essentialconstituent, a synthetic precipitated alkaline earth metal silicate, theamount of said filler being about 10 percent to 25 percent, based on thedry weight of said mat, said stereotype mat being characterized by highplasticity when moist.

4. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler and having a water content of about 10 percent to50 percent based on the total weight of said mat, said filler containingas an essential constituent, a synthetic precipitated alkaline earthmetal silicate, the amount of said filler being about.

10 percent to 25 percent, based on the dry weight of said mat, saidstereotype mat being characterized by high plas ticity when moist.

5. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellu-' 1 lose fibers and discreteparticles of a filler, said filler containing as anessentialconstituent, a synthetic alkaline earth metal silicate precipitated froman aqueous solution of an alkaline earth metal compound by an alkalimetal silicate, said stereotype mat being characterized by highplasticity when moist.

6. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler, said filler containing as an essentialconstituent, a synthetic precipitated alkaline earth metal silicatewhich has been dried and.

ground, said stereotype mat being characterized by-high plasticity whenmoist. v v

7'. A stereotype dry mat comprised uniformly through-. out the thicknessthereof ,of a co-felted mixture .of cellulose fibers and discreteparticles of a filler, said filler con taining as an essentialconstituent, a synthetic precipitated alkaline earth metal silicate,said stereotype mat having a release-promoting coating upon the moldingand casting surface thereof, said stereotype mat being characterized byhigh plasticity when moist.

8. A stereotype dry mat comprised uniformly throughout the thicknessthereof of a co-felted mixture of cellulose fibers and discreteparticles of a filler, of said filler containing, as an essentialconstituent, a synthetic alkaline earth metal silicate exhibiting thefollowing characteristics: a surface area of at least 10 square metersper gram as determined by the low temperature nitrogen adsorptionmethod, and a substantial amount of said silicate being in the amorphousstate as determined by the presence of an amorphous ring on the'X-raydiffraction pattern, said stereotype mat being characterized by highplasticity when moist.

References Cited in the fileof this patent UNITED STATES PATENTS

8. A STEREOTYPE DRY MAT COMPRISED UNIFORMLY THROUGHOUT THE THICKNESS THEREOF OF A CO-FELTED MIXTURE OF CELLULOSE FIBERS AND DISCRETE PARTICLES OF A FILLER, OF SAID FILLER CONTAINING, AS AN ESSENTIAL CONSITUTENT, A SYNTHETIC ALKALINE EARTH METAL SILICATE EXHIBITING THE FOLLOWING CHARACTERISTICS: A SURFACE AREA OF AT LEAST 10 SQUARE METERS PER GRAM AS DETERMINED BY THE LOW TEMPERATURE NITROGEN ADSORPTION METHOD, AND A SUBSTANTIAL AMOUNT OF SAID SILICATE BEING IN THE AMORPHOUS STATE AS DETERMINED BY THE PRESENCE OF AN AMORPHOUS RING ON THE X-RAY DIFFRACTION PATTERN, SAID STEREOTYPE MAT BEING CHARACTERIZED BY HIGH PLASTICITY WHEN MOIST. 